The present invention relates to an apparatus for the analysis of gaseous media, the apparatus including at least one microwave transmitter, at least one measuring cell having at least one gas inlet and one gas outlet, a detector and at least one high voltage Stark electrode disposed in the measuring cell and insulated therefrom.
It is known to analyze gaseous media, possibly also after conversion of a solid substance or a liquid into the gaseous state, by absorption of microwaves within certain characteristic frequency ranges by the excitation of rotational transitions in molecules of the media to be examined. In order to reduce the spectroscopic line width, the examination takes place in the low pressure range.
The absorption lines are split by utilizing the Stark effect, an alternating Stark voltage preferably being applied to increase detection sensitivity. Such a process is highly selective in principle but does not require prior changes, such as ionization or chemical reactions of the substances to be examined.
In the prior art devices, the measuring cells are overdimensioned. Moreover, extensive memory effects have been noted. These effects are manifested in that a once measured gas can still be detected even after a certain time has elapsed. The overdimensioning of the absorption cell is required, in particular, because the high voltage Stark electrodes or the Stark septum can be inserted only into cells having an overdimensioned cross section. Moreover, the Stark septum employs carrier materials, such as Teflon, which may also absorb gases, which likewise results in increased memory effects. The gas intake and outlet are also of a disadvantageous configuration; they have considerable dead space, which likewise increases the memory effects.